(Reuters) – Missouri Governor Jay Nixon said on Friday the investigation into the death of an unarmed black teenager shot by a police officer in a St. Louis suburb needs to be completed before drawing conclusions.

His comments came after local police said the teen, Michael Brown, was the prime suspect in a store robbery in Ferguson minutes before his death.

“Nothing should deter figuring out how and why Michael Brown was killed,” Nixon said at a press conference.

The U.S. Department of Justice and St. Louis County Police are investigating the death of Brown, who was 18.

Captain Jay Johnson of the Missouri Highway Patrol, who took over control of security in Ferguson the previous day, said there were no arrests during protests on Thursday night and no tear gas used after his officers replaced local police.